1. Field of the Invention
The invention relates to a self-regulating heating device with a lamellar resistance-heating body made of an electrically conducting ceramic material with a positive temperature coefficient. More particularly, it relates to such a heating device which comprises a heating body that is wedged together with electrical insulating bodies into a wedge-shaped slot of a body to be heated. The heat generated in the heating body is dissipated through said insulating bodies.
2. The Prior Art
Self-regulating heating devices of the aforementioned type are known (German Patent Specification 28 16 076), in which the resistance-heating body made of electrically conducting ceramic material is configured as a plane parallel lamina. In order to achieve a wedging effect, which is intended to result in a proper contact of the heating device components associated with the dissipated of heat, a special wedge body is provided or the insulating bodies arranged at both sides of the resistance-heating body are themselves wedge-shaped in construction. This arrangement, in the former instance, requires at least one additional part, specifically, a special wedge body. It also increases the number of the transition surfaces lying in the thermodiffusion path, which fact results in an undesired increase in thermal resistance and which is detrimental to the heating devices of the aforementioned kind because it negatively affects self-regulating efficiency. With the second aforementioned configuration of the heating device known in the art, in which both insulating bodies arranged on both sides of the heating body are themselves wedge-shaped in construction, the use of two wedge bodies results in relatively high fabrication costs. Also the wedge shape of the insulating bodies additionally results in the fact that these insulating bodies exhibit varying thickness at various locations which produces substantial variations in thermal resistance, resulting in uneven dissipation of the heat generated in the heating body which can bring about local electrical overloads.
German Patent Specification 25 43 314 discloses a two-layered heating body in which both layers are wedge-shaped in construction and are laminated together to a plane parallel body. The one layer consists of PTC materaial, the other layer being of common resistance material; through this configuration the dissipation of thermal energy, viewed over the surface of the heating body, is intended to assume different values.